I read 4 other answers that were pretty much spot on. What was missed is why our bullets are made the way they are. Virtually all ammunition is made of brass. There is some aluminum or steel ammunition out there, but they are oddities among shooters. read more
Cases used to be made of nitrated linen. These were used in the early breech loaders, like the Sharps. The linen was soaked in potassium nitrate(saltpeter) to make it combustible. read more